Bottle having ribbed bottom

ABSTRACT

A method of and apparatus for making a concave bottom on a blown thermoplastic container, and a container having such a bottom. A blowable pre-form is initially expanded against a composite mold surface defined by the end faces of a plurality of concentric tubes surrounding a central actuating rod. The rod and the tubes are initially telescopically positioned to define a composite concave surface, so that a first convex bottom is blown. Subsequently, the rod and tubes are actuated telescopically to progressively invert the convex bottom to a concave shape. The end faces of the tubes may be grooved to define reinforcing ribs in the concave bottom wall, if desired. 
     The container has a concave bottom wall of improved resistance to deformation under internal pressure. This is accomplished by forming a support ring at the juncture of a pair of oppositely directed inner and outer bottom walls, the juncture of the walls defining an included angle which is equal to or less than 90° and the internal radius of the support ring is equal to or less than four times the thickness of the walls.

This is a divisional of application Ser. No. 587,011 filed June 16,1975, now U.S. Pat. No. 4,036,926, issued July 19, 1977.

BACKGROUND OF THE INVENTION

This invention relates to the manufacture of bottles or containers ofthermoplastic materials for the retention of fluids under pressure, suchas carbonated beverages or the like. Recently, various thermoplasticmaterials have been developed which are capable of retaining carbondioxide and which are blow-moldable into suitable containers. Suchmaterials include poly(ethylene terephthalate) or PET, or nitrile basedresins known as LOPAC, a registered trademark of Monsanto Company, ornitrile-group-containing monomers of the type disclosed in U.S. Pat. No.3,873,660.

Such a bottle generally consists of a shoulder portion with acap-receiving finish, a side wall or main body portion, and a bottomwall joined to the side wall. Pressure-retaining bottles are generallyof cylindrical overall contour, but the present invention is applicableto bottles of other than cylindrical contour. For purposes of simplicityof description, such terms as "cylindrical", "annular", etc. are hereinutilized, but it should be understood that these terms are merelydescriptive, not limiting, in a geometric sense.

One primary problem which is encountered in blow-molding thermoplasticmaterials to form bottles capable of retaining CO₂ and other gases underpressure resides in the provision of a bottom shape capable of servingas a bottle support, while resisting deformation under pressure.

One suitable bottom shape is a simple, outwardly hemispherical shape,but this requires a separately applied, outer peripheral support to makethe bottle stand upright. A less expensive, more practical shape resultsfrom the inversion of the outwardly hemispherical shape to an inwardlyconcave or "champaign bottom" shape. The transition region located atthe juncture of the cylindrical bottle side wall with the inverted,concave bottom forms a seating ring upon which the bottle is supportedin an upright position. Much effort has been devoted to the design ofinverted, concave bottoms of this type, and many different methods andmany different molds have been developed.

To reduce the creep characteristics of polymeric materials underinternal pressure, the material is oriented during the bottle formation,requiring blowing at a reduced temperature. Attempts to form a concavebottom by directly inflating a parison in a blow mold of the finalbottle shape have failed. Under these blowing conditions, the materialsimply "bridges over" the sharp curvatures required in the mold to forman adequate seating ring, and the material stretches and thins out inthe region where the greatest strength is required. As a result, seatingrings deform under internal pressure to reduce the seating ring diameterand to change the pressure-resistant characteristic of the concavebottom.

It has been proposed that an initial outwardly convex bottom be blownwhich is then inverted to form a final concave bottom. Those methods andapparatus heretofore proposed either (1) require the utilization of aseparate inversion mold and reheating of the initial bottom or (2)simply push a convex die against the outwardly convex bottom. Neithertechnique has solved the problems inherent in the requirements of sharpcurvatures in the transition zone and of adequate material thickness atthe seating ring.

As a result, the prior art has not yet evolved a method and apparatusfor forming a concave, pressure-resistant bottom for a thermoplasticcontainer capable of retaining fluids under pressure.

SUMMARY OF THE PRESENT INVENTION

The present invention, in essence, provides a novel bottom shape for apressure-resistant thermoplastic container, and also provides novelmethods and apparatus for the manufacture of such a container.

Generally, the present invention utilizes an overall blowing apparatusand method such as that disclosed in Rosencrantz U.S. Pat. No.3,599,280. In this patent, a thermoplastic parison is heat-conditionedto a desired temperature at which the parison is blowable, and thematerial will be oriented biaxially upon blowing at such temperature.The parison is supported on a mandrel such as that illustrated inSeifert U.S. Pat. No. 3,865,530, the mandrel being extensible duringblowing to promote the orientation of the material and to accuratelyposition the parison internally of the blow mold.

The blow molds of these earlier patents are modified to provide a moldbottom which is convertible from an initial concave shape to a finalconvex shape. This is accomplished by making the mold bottom as acomposite of a plurality of tubular elements telescopically movablerelative to one another and telescopically movable relative to a centeractuating rod. The mold bottom is defined by the end faces of theconcentric tubes and the rod. These end faces are are initiallypositioned to cooperatably define a concave shape forming an extensionof the remainder of the blow mold, and the parison is inflated againstthis composite shape to provide a convex bottom portion on the blownparison or pre-form. After initial blowing, and while the parisoncontains sufficient residual heat to be readily reformable, the centralrod is actuated to project into the mold, and the rod actuates, insequence, the concentric, telescopically movable sleeves to varyingextents and in the same direction. As a result, the convex bottom isinverted into a concave shape.

By actuating the bottom sections in sequence, the initial convex bottomof the blown pre-form is sequentially folded back into its final concaveconfiguration. Further, the ends of the sleeves contour the blown bottomto define circumferential reinforcing ribs thereon. The ends of thesleeves can also be grooved, if desired, to provide radial reinforcingribs at the exterior surface of the bottom wall.

As a result, a blown bottom is defined which has a reinforcing supportring formed at the juncture of inner and outer bottom walls, this ringbeing of uniform wall thickness, of reduced radius and defined betweensteeply inclined inner and outer walls for maximum structural rigidity.

ON THE DRAWINGS

FIG. 1 is a general assembly view, showing, in elevation, the generalarrangement of an apparatus of the present invention capable of carryingout the method of the present invention;

FIG. 2 is a sectional view, with parts, shown in elevation, illustratingthe support of a parison or pre-form on a mandrel;

FIG. 3 is an enlarged, partial view similar to FIG. 1, illustrating ingreater detail the blow mold of the present invention and the initialinflation of the pre-form in the blow mold;

FIG. 4 is an enlarged fragmentary sectional view taken along with plan4--4 of FIG. 3, and illustrating the specific blow mold bottomconstruction of the present invention and the carrying out of an initialstep of the method of the present invention;

FIG. 5 is a fragmentary perspective view of the bottom of the blownpre-form of convex shape, carried out by the apparatus and method ofFIG. 4;

FIG. 6 is a fragmentary elevational view in perspective of the apparatuspositioned as illustrated in FIG. 4;

FIG. 7 is a view similar to FIG. 4, illustrating the final position ofthe apparatus and the final carrying out of the method of the presentinvention to reform the bottom to a concave configuration;

FIG. 8 is an elevational view, in perspective, of the container bottomafter the performance of the method step of FIG. 7;

FIG. 9 is a view similar to FIG. 4, illustrating a different form ofapparatus for forming a concave bottom, having an innermost convexportion;

FIG. 10 is a view similar to FIG. 7, illustrating the apparatuspositioned to carry out the bottom reforming step of the method;

FIG. 11 is a fragmentary view, similar to FIG. 10, illustrating a methodand apparatus for providing radial reinforcing ribs in the final convexbottom;

FIG. 12 is a fragmentary elevational view of a container bottom havingsuch radial reinforcing ribs; and

FIGS. 13 and 14 are fragmentary sectional views of two bottomconfigurations of containers of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown on the drawings, and specifically in FIG. 1, a blow moldingapparatus of the type fully described in U.S. Pat. No. 3,599,280 isillustrated. Reference to said U.S. Pat. No. 3,599,280 is made for fulldetails, which need not be repeated here.

Specifically, the apparatus includes a rotary table 20 carrying avertical post 21 surmounted by a support flange 22. The table 20 carriesa plurality of vertically-extending support posts 23, only one of whichis illustrated. This post 23 is supported in vertical position by theflange 22 and an upper flange 23 spaced above the flange 22. Interposedbetween the flanges is a blow mold indicated generally at 25.

The mold assembly 25 comprises a pair of openable and closable blow moldsections of the "book"-type, having interdigitated hinge sleeves 26journalled on the vertical post 23. The mold sections are openable andclosable by actuating means (not shown) described in U.S. Pat. No.3,599,280.

The upper-free end of the post 23 carries a radial, projecting arm 27supporting, at its outer end, a vertical actuating cylinder 28, thepiston 29 of the cylinder 28 carrying a bottom mold assembly 30. Thisbottom mold assembly 30 is axially aligned with the open topped blowmold cavity 31 defined by the blow mold 25. A lower radial support arm32 carries a second actuating cylinder 33 having an upwardly projectingactuating rod 34 surmounted by a blow air supply head 35. When actuatedby the cylinder 33, the block 35 abuts the under surface of a secondradial lower arm 36 surmounted by a mandrel support 37. Mounted on thesupport 37 is a mandrel block 38 having a central bore 39 through whicha mandrel indicated generally at 40 projects. This mandrel 40 isvertically aligned with the mold bottom assembly 30 and with the moldcavity 31, the block 38 being clamped in position to close the loweropen end of the mold cavity 31 when the mold halves are closed, with themandrel 40 projecting axially into the mold cavity 31, as illustrated inFIGS. 1 and 3.

As explained in detail in U.S. Pat. No. 3,865,530, the mandrel 40comprises a lower elongated tubular section 41 surmounted by acup-shaped element 42. As air under pressure enters the mandrel throughthe lower tubular portion 41, the upper cup-shaped element 42 movesvertically to follow the axial expansion of the parison.

As best illustrated in FIG. 2 of the drawings, a heated, thermoplasticpre-form or parison 45 is positioned on the mandrel 40. This parison 45includes a lower threaded neck or finish portion 46 abutting the block38 and engaged by the mold 25 when the mold halves are closed. An uppertubular portion 47 of the parison surrounds the mandrel 40 and issurmounted by a closed, generally hemispherical parison end 48 fromwhich the bottom of the container will be formed, as hereafter morefully described in detail. This closed end 48 of the parison ispositioned in the mold cavity 31 short of the open upper end 49 of themold cavity and in registry with the upper mold bottom assembly 30.

The mold bottom assembly 30 is best illustrated in FIGS. 3, 4, 7, 9 and10. From FIG. 3, it will be seen that the mold bottom assembly 30comprises a mold bottom block 50 having a lower aperture 51 whichregisters with the aperture 49 of the mold cavity 31. This aperture 51is contoured to blend into a conical surface 52 which, in turn,terminates at a cylindrical bore 53 extending upwardly through the block30. A guide sleeve 55 surmounts the block 50 and has a bore 56 forming acontinuation of the bore 53. The guide sleeve 55 is radially slotted asat 57, for a purpose to be hereinafter more fully described. The guidesleeve has superimposed thereon an actuating cylinder 60 encompassing afluid-actuated piston 61 having a piston rod 62 illustrated in FIG. 3 inits retracted position and extensible downwardly into the bore 56 of theguide sleeve 55. The cylinder 60 is provided with fluid ingress andegress means (not shown) for actuating the piston 61 between itsillustrated upper retracted position and its lower, extended position.

The cylinder 60 is secured to the actuating piston rod 29 of the uppercylinder 28, heretofore described, by mounting block assembly 63. Uponactuation of the cylinder 28, the entire upper mold assembly comprisingthe mold block 30, the guide sleeve 55, the actuating cylinder 60 andthe mounting block 63 are actuated vertically from their retractedposition of FIG. 1 to their lowered, extended position of FIG. 3.

Referring now to FIG. 4 of the drawings, it will be seen that the lowerend of the piston rod 62 has a reduced mounting portion 64 projectingtherefrom, and this mounting projection is secured to a central rod 65which is cylindrical in contour and which projects downwardly throughthe guide sleeve bore 56 to depend into the bore 53 of the bottom moldblock 50. This rod 65 is provided with an upper radial slot 66 and witha lower radial slot 67. Positioned in the upper slot 66 and projectingradially through the aligned slots 57 in the guide sleeve 55 is a fixedkey indicated generally at 70. The central portion of the key 70,indicated at 71, is of reduced axial extent and registers with the slot66 in the central rod 65. The rod 65, thus, is movable axially uponactuation of the cylinder assembly 60, such movement being accommodatedby movement of the key 71 in the slot 66.

Surrounding the rod 65 and telescopically interposed between the sleevebore 56 and the rod is a series of telescopically assembled sleeves72,73,74, each such sleeve having a radial slot 72a,73a,74a therein toreceive the key 70 therethrough, the key having upper and lower steppedsurfaces 75,76,77 thereon for abutting the edges of the slots 72a,73a,and 74a respectively.

A second, lower key 80 is positioned in the lower slot 67 of the rod 65.This key is provided with a central portion 81 which fits snugly withinthe slot 67 of the rod 65, and this key is radially sized to fit withinthe bore 53 of the mold block 50. Each of the sleeves 72,73,74 isprovided with a second radial slot 72b,73b,74b, respectively, receivingthe outer portions of the key 80 therethrough, the key 80 being providedwith upper and lower stop surfaces 82,83,84 engageable with the upperand lower edges of the slots 72b,73b,74b, respectively.

The function of the key 80 is to actuate each of the sleeves 72,73,74 insequence as the rod 65 is lowered or raised by the cylinder 60.Comparing FIGS. 4 and 7, it will be seen that lowering of the rod 65similarly lowers the key 80. The inner sleeve 72 will be actuateddownwardly when the lower slot edge 74b is contacted by the lower keyabuttment surface 82. Upon further movement, the sleeve 73 will beactuated downwardly by abuttment between the key edge 83 and the slotedge 73b, while the same abuttment between the key surface 84 and theslot edge 74b will accomplish vertically downward displacement of theouter sleeve 74.

The function of the upper key 70 is to serve as a stop for the downwarddisplacement of the central rod 65 and each of the sleeves 72,73,74.Downward motion of the rod 65 ceases when the slot edge 66 contacts theupper abuttment surface of the central portion 71 of the key 70. At thesame time and in the same manner, the key abuttment edges 75,76,77contact the upper extremities or edges of the sleeve slots 72a,73a,74a,respectively.

Thus, the lower key 80 serves to axially displace the sleeves 72,73,74axially as a consequence of the displacement of the rod 65. The upperkey 70 serves as a stop to position the rod 65 and the sleeves 72,73,74in both of their extreme axial positions of FIG. 4 and of FIG. 5.

It will be noted that the lower end of the rod 65 is convex and slightlyrounded to a partial spheroidal shape, as at 85. The ends of the sleeves72,73,74 are chamfered out their outer peripheries, as at 72c,73c and75c, for a purpose to be hereafter more fully described.

Turning now to the operation of that embodiment of the inventionillustrated in FIGS. 3 through 8, it will be seen from FIG. 3 that theparison 45 of FIG. 2 has been blown or inflated to the shape of the moldcavity 31. The slidable sleeve 42 of the mandrel 40 is extended with theparison as it is blown. During blowing, the rod 65 and the sleeves72,73,74 occupy their positions as illustrated in FIG. 4, i.e., with thecylinder 60 actuated to retract the piston 61, thereby positioning therod 65 and the sleeves 72,73,74 in abuttment with the lower abuttmentsurfaces of the key 70.

As seen in FIG. 4, the parison is blown and expanded into contact withthe conical wall 52 of the mold bottom block 50 and against the undersurfaces of the retracted elements 65,72,73,74 to form a bottom 86 ofoverall convex configuration against the end surfaces of the sleeves72,73,74, the center of this bottom being of slightly concaveconfiguration, as at 87, due to its contact with the rounded lower endof the retracted rod 65. Further, it will be noted that the bottom 86,under the pressure of the blowing medium, flows into the spaces providedby the chamfered ends 72c,73c,74c of the sleeves to providecircumferential ribs 88 circumscribing the exterior surface of theconvex bottom.

Immediately after the blowing step and while the heated thermoplasticblown bottom is still capable of elastic deformation, the cylinder 60 isactuated to move the piston 61, the piston rod 62, and the rod 65downwardly. At the same time, the mandrel is retracted downwardly. Whenthe rod 65 and the key 80 have moved sufficiently to abut the keysurface 82 with the lower edge of the slot 72b, the inner sleeve 72 ismoved downwardly. Further movement of the rod 65 and the key 80successively brings the key surfaces 83 and 84 into contact with thesleeve slot edges 73b and 74b to likewise displace the sleeves 73 and 74downwardly. This downward displacement continues until the upper edgesof the slots 66,72a,73a and 74a abutt the upper abuttment surfaces71,75,76,77 of the upper key 70. At this time, the rod 65 and the sleeve72,73,74 have assumed their positions illustrated in FIG. 7, where theends of the sleeves 72,73,74 now define an overall convex configuration.The displacement of these elements displaces the initial convex bottom86 of the container to the concave configuration illustrated in FIG. 7and indicated by reference numeral 90.

The initial actuation of the rod 65 followed by the successive,sequencial actuation of the sleeves 72,73,74 results in the initialdisplacement of the center of the convex bottom 86 with the bottom beingsuccessively actuated radially outwardly from the center. As a result,the final motion of the outermost sleeve 74 folds the juncture of thatportion 91 of the bottom lying against the conical surface 52 and theconcave portion 90 of the bottom into a sharp annular joining portion 92of quite small radius. This annular portion 92 constitutes the extemeaxial edge of the bottle and provides an annular support ring ofdesirable configuration, as will be hereafter more fully explained.

The entire assembly of the rod 65, and the sleeve 72,73,74 are retainedin their configuration of FIG. 7 until such time as the blown containerhas been cooled to a self-sustaining state. At that time, the uppercylinder 28 is actuated to retract the entire bottom mold assemblyupwardly. At this time, the mold 25 may be opened and the finishedbottle removed.

In that embodiment of the invention illustrated in FIGS. 9 and 10, amold bottom is formed which is of slightly different configuration. Inthis instance, the center rod 65 is provided with a concave free end 95rather than the convex lower end 85 described in connection with theembodiments of FIGS. 4 and 7. The sleeves 72,73,74 are identical, as isthe lower key 80. The only difference is that the final bottom wall isprovided with a concave central depression or dimple 96, surrounded byan annular return portion 97 joining the portion 96 to the concave wall90 heretofore described. This portion 96 may have certain advantages issome applications since, it reduces the depth of the push-up of thebottom wall into the container where a large seating ring 92 is requiredfor support stability.

It will be recalled that the blowing of the bottom wall 90 against thefree, chamfered ends of the sleeve 72,73,74 created ribs 88circumferentially of the wall 90. In FIGS. 11 and 12, there isillustrated another variation, wherein, the ends of the sleeves areradially slotted as at 72d,72d,74d to form radially extending ribs 89 ofincreased wall thickness, these radial ribs 89 cooperating with theperipheral ribs 89 to form a grid-type reinforcement for the bottom wall90.

One of the primary objectives of the present invention is the provisionof an improved container having a bottom wall of enhancedpressure-resistant characteristics. Such a bottom wall is specificallyillustrated in FIGS. 13 and 14. The remainder of the container is quiteconventional and includes a side wall 100 of cylindrical configurationor of any other desired configuration, this side wall being surmountedby a shoulder and a dispensing opening (not shown) and which can be ofany desired configuration.

The specifically improved bottom, pressure wall of the present inventionincludes an exterior peripheral wall 101 which is preferably conical inconfiguration, the wall 100 terminating in a return portion 102 defininga seating ring located inwardly of the wall 100. The central portion 103of the bottom wall is of overall concave configuration and may extendupwardly to a central concave portion 104 (FIG. 13) or may extendupwardly to a depressed convex central portion 105, as explained inconjunction with FIGS. 9 and 10 above. The compound concave-convex shapeof FIGS. 9 and 10 has the advantage of not reducing the capacity of thecontainer, and so is preferred in some instances.

The conical wall 101 may be defined as having a slope angle A withrespect to the horizontal B of 45° or better. Alternatively, the slopeangle of the wall 101 may be defined with reference to the side wall 100of the container, and this included angle C is at least 135°. Therelatively great steepness of the slope angle A increases the rigidityof this wall against bending under the pressure generated internally ofthe container. The lower side wall 101 need not be conical but theradius should be as great as possible so as to approach a conicalconfiguration.

The seating ring region 102 has a radius of curvature which is as smallas possible. This radius of curvature may be defined as the ratio of theradius of curvature D to the wall thickness of the container bottom, andthis ratio should be as small as possible and preferably less than four.In other words, the radius of curvature of the portion 102 is not morethan four times the average wall thickness of the container bottom.

The slope angle E of the concave portion 103 is also as great aspossible to enhance bending resistance in this region. Again, a slopeangle of at least 45° is preferred. Finally, the included angle Fbetween the slope angle of the outer wall 101 and the slope angle of theinner wall 103 is preferably less than 90°, again, to increase thebending resistance.

I claim:
 1. In a bottle for the retention of fluids under pressure,having a side wall surmounted by a dispensing opening, a generallyconcave bottom comprising:an outer conical tapered wall and an innerarcuate concave wall lying at an acute angle relative to said outerwall, said walls being jointed by an arcuate support ring, a pluralityof concentric annular strengthening ribs formed in said inner wall atthe exterior thereof, and a plurality of additional radial ribs alsoformed in said inner wall, said radial ribs intersecting said annularribs and projecting inwardly therebeyond to additionally strengthen theinner wall interiorly of said annular ribs.
 2. In a bottle as defined inclaim 1, the further improvement wherein said bottom inner wall is ofsmoothly arcuate concave shape.
 3. In a bottle as defined in claim 1,the further improvement wherein, said bottom inner wall is of compoundconcave-convex shape having an exterior annular concave portion and acircular central convex portion thereof depending toward the supportring and said radial ribs bridging the juncture between said concave andconvex portions.
 4. In a bottle for the retention of fluids underpressure, a side wall surmounted by a dispensing opening and having agenerally concave bottom, said concave bottom comprising:inner and outertapered walls lying at an acute angle relative to one another and joinedby an arcuate support ring, said tapered walls concentricallysurrounding an arcuate central portion which is convex to reduce theheight of the bottom, and a plurality of concentric circularstrengthening ribs formed in said inner wall and a plurality of radialstrengthening ribs extending radially inwardly throughout the radialextent of said inner wall and projecting inwardly beyond said concentricribs to bridge the juncture of said inner wall and said locally convexcentral portion.